Mineral beneficiation by decompression scalping

ABSTRACT

Certain minerals, particularly weathered phosphate pebble, are treated to remove significant quantities of impurities by pressurizing a slurry thereof to about 25-100 psig, preferably 30-60 psig for weathered phosphate pebble, and passing the pressurized slurry through a nozzle to the atmosphere to provide sudden release of pressure. Weathered and other encrusted minerals treated in this manner are beneficiated by the dissolution and particularly by the erosion of impurities primarily encrusted on the mineral. The erosion and collapse of the crust is believed to be caused at least partly by the sudden flow of water held in the pores of the crust.

United States Patent [191 Ribas 51 May 6, 1975 MINERAL BENEFICIATION BY DECOMPRESSION SCALPING [75] Inventor:

[73] Assignee: United States Steel Corporation, Pittsburgh, Pa.

[22] Filed: Sept. 13, 1973 [21] Appl. No.: 396,952

Roger S. Ribas, Decatur, Ga.

Primary ExaminerRoy Lake Assistant ExaminerDeWalden W. Jones Attorney, Agent, or Firm-William L, Krayer 5 7 ABSTRACT Certain minerals, particularly weathered phosphate pebble, are treated to remove significant quantities of impurities by pressurizing a slurry thereof to about 25100 psig, preferably 30-60 psig for weathered phosphate pebble, and passing the pressurized slurry through a nozzle to the atmosphere to provide sudden release of pressure. Weathered and other encrusted minerals treated in this manner are beneficiated by the dissolution and particularly by the erosion of impurities primarily encrusted on the mineral. The erosion and collapse of the crust is believed to be caused at least partly by the sudden flow of water held in the pores of the crust.

7 Claims, 2 Drawing Figures PATENTEDMAY ems 8/ Z MIG SE6 Tl ON 38 A FLOTAT/ON 1 MINERAL BENEFICIATION BY DECOMPRESSION SCALPING BACKGROUND OF THE INVENTION Weathering effaces the texture of the rocks and segregates their chemical components. It occurs in the top 100 to 200 feet of the earths crust. Segregation of large masses of single minerals is usually a result of such weathering.

Disintegration and chemical decomposition of the earths crust work simultaneously, but disintegration is likely to extend deeper than decomposition. The upper layers, frequently colored red or brown by ferric iron, gradually change into lighter colored, more or less softened and disintegrated rock. Except in the easily soluble rocks, the decomposition is never complete. Even in the fine soils, abundant grains of the original minerals remain unaltered. Texturally, such rocks may show extreme porosity and vesicularity with open spongelike texture indurated and maintained by secondary minerals and cements, as in the classic laterite of India.

Lateritic weathering normally occurs in tropical countries, and is a particularly severe type of weathering. Serpentine and limestone are typical rocks attacked by lateritic weathering. In general, the top layer of a typical laterite is essentially a mixture of the hydroxides of iron and aluminum with more or less free silica. The iron has a strong tendency to segregate into pellets or lumps. The iron ore from Mayari, Cuba is a laterite exceptionally rich in iron and nickel. Laterities may or may not contain bauxite of economic value. In Jamica, bauxite-rich laterites are mined.

The processes of weathering result in concentrations of phosphate, iron, nickel, alumina, manganese, barite, and zinc. Such deposits are usually of economic importance.

In the Florida phosphate fields, lateritic weathering is known to occur near the drainage basins of the Peace and Alafia Rivers, where the upper part of the Bone Valley apatite formation is irregularly transgressed by a white zone of leaching and alteration the aluminum phosphate zone. Pockets of weathered material have been found which originally were present at the base of the zone disseminated within the matrix. This is apparently due to cross bedding. Therefore, some of the apatite pebble shows incipient leaching and alteration. Whenever graded-bedded pebble rock of the lower Bone Valley is altered, coarse vesicularity with relic-graded texture results. One of the main characteristics of this weathered crust on the phosphate pebble surface is its fine porosity. The crust usually contains 30-50% of the total iron, aluminum, and magnesium found in the pebble.

In Florida phosphoric acid production, beneficiated phosphate rock is normally digested with sulfuric acid to extract the phosphate values. Increased production and decreasing high-grade reserves of phosphate rock have forced the use of rock containing higher levels of iron, aluminum, and magnesium impurities, mainly the oxides. Production of phosphoric acid with relatively high impurity levels creates a chain of problems carrying through to the manufacture of finished fertilizer products.

During phosphate rock digestion with sulfuric acid, problems are created by increased slurry viscosities and poor gypsum crystal growth, as well as greater sulfuric acid consumption. Concentration of phosphoric acid to a nominal 54% P 0 merchant-grade product results in preciptation of complex iron and aluminum phosphates such as (Fe, Al) KI-I (PO4) .4H O and others. Even after centrifugation of the concentrated acid, post precipitation of solids occurs on extended storage. The volumes of valuable sludge acid, generated due to high levels of impurities, creates problems in disposal in useful fertilizer products. For example, phosphoric acid is used in the manufacture of triple superphosphate, and high levels of iron and aluminum in the acid result in high mixing viscosities, extended cure times, and a product having a high free-acid content.

In the manufacture of fluid fertilizers, high impurity levels (particularly magnesium) result in precipitates forming during preparation and storage, and in increased viscosities. As a result, it is generally necessary to add some electric-furnace phosphoric acid to lower the average impurity level. This results in higher-cost products.

High impurity levels also affect the properties and production 'of superphosphoric acid, usually containing more than 68% P 0 I-Iigher evaporation temperatures are required, precipitated condensed phosphate solids are difficult, if not impossible, to remove, and polyphosphate-containing fluid fertilizers are difficult to produce and have a relatively short storage life.

From an economic standpoint, it is desirable to accomplish reduction in the iron, aluminum, and magnesium impurities during beneficiation of the phosphate rock rather than to process a high-impurity rock through a phosphoric acid manufacturing plant and then attempt to cope with the removal of impurities or the undesirable physical properties of the final fertilizer products.

Several types of equipment and techniques known to those skilled in the art were investigated to overcome the problems stated above. Since they may serve as a summary of the major prior art methods, a summary of the results is given below.

Grinding to liberate the impurities, followed by amine flotation to separate phosphate, was first evaluated. Rod-mill grinding was selected, since this method generates a minimum of fines and, therefore, minimizes phosphate losses. Conventional flotation procedures are economically and practically applicable above a certain particle-size range. The generation of fine particles increases the phosphate losses in the process and the consumption of reagents. A single cationic flotation step was selected rather than the standard anionic flotation followed by the cationic flotation, since the grade of the pebble was too high for two steps of flotation, and the cationic step is more selective in impurity removal. A large amount of impurities reported to the fines for a concentration ratio of about 3 to 2, but the phosphate loss through fines was unacceptable. Furthermore, the iron and aluminum impurities were actually concentrated in the amine flotation step. Perhaps further investigation might have reversed this trend, but the high grinding losses as fines were prohibitive.

At this point there was evidence that a sizable reduction in the rock iron and aluminum could be achieved by physical, or combined physical-chemical, methods which would selectively remove the weathered portion without appreciably changing the structure of the unweathered apatite. Phosphate pebble is usually recovered and classified as fine, medium, and coarse pebble, with Tyler screen particle sizes of l 6+20, 6+1 6, and

+6, respectively. Particle sizes in each general group are often varied, depending upon operating conditions.

Coarse pebble was given one pass through an impactor, and screen analyzed. Considerable selectivity of removal was obtained, but the method was not applicable to medium pebble which, for the particular mine, represented roughly 90% of the total pebble. This was due to the lower kinetic energy of particles with diminishing diameters.

At the same time, it was found that substantial alu- 1O mina could be removed from the phosphate rock by sodium hydroxide leaching. Although this could be applicable to the of the rock highest in alumina, its use was limited by reagent cost and the relative high volume of aqueous slurries that must be handled.

Many ore beneficiation operations include an attrition scrubbing step using agitator-type scrubbers, where grinding would be detrimental due to degradation of crystals or generation of excessive slimes. In

testing agitation scrubbing laboratory results were encouraging, although retention times were high which is a serious disadvantage since large-scale installations consist basically of agitated tanks. High retention times in agitated tanks translate to a high capital investment to handle large tonnages of material.

The system of explosive grinding of minerals at high pressures (2,000 psi) was studied by the US. Bureau of Mines in 1933. Table I outlines the essential differences between Decompression Scalping (my invention) and Explosive Grinding. To the best of my knowledge,

4 closed-circuit grinding of the ore. Pryor 2. D. Jigs, hy-

draulic traps, unit flotation cells, where strakes are used. Use of a coarse screen to protect a fine ore. Also, removal of superficial oxidized layer from wirebar copper which is to be used in drawing of fine wire.

The objective of most comminuting operations in the mineral industry is the liberation of the valuable minerals from the ore. This is accomplished by crushing or grinding the ore until the entire mass has been reduced to particles small enough that the probability of any single particle containing more than one mineral is slight. In the course of such an operation, many liberated particles, both coarser and finer than the nominal size of the final product, are nevertheless reduced further. Since fracture of such particles does not improve liberation of the valuable mineral and may even result in the formation of detrimental slimes, it represents unnecessary work and may be harmful both economically and technically to subsequent separation operations.

Prior to the present invention, it has been known to utilize pressure in various ways to break up, comminute, grind, and otherwise liberate minerals from ores of various kinds. For example, Dean in US. Pat. No. 2,078,933 uses steam under pressure which is suddenly released, resulting in an explosion of the ore particle. Cohn, in US. Pat. Nos. 3,253,791 and Re 25,965 employs a slurry of a relatively homogeneous mineral, pressurized at greater than 100 psig. and passed to an area of lower pressure. Carcreek, in US. Pat. No. 2,864,560 also uses steam, and Cavanaugh, US Pat. No. 3,163,518 working to remove silicon from iron ore, utilizes low pressures in combination with NaOH treatment but without a sudden release of the pressure.

Also of interest is a paper presented at the 1972 Mining Convention of the American Mining Congress, September 1972 by William J. Cavanaugh, entitled The Snyder Process A Breakthrough in Comminution which apparently uses intermittent pressure cycles of some kind but not revealed in detail by the author.

TABLE I PROCESS DIFFERENCES DECOMPRESSION SCALPING EXPLOSION GRINDING Main Action Ore Pressure Medium Mechanism Applicability Equipment Velocity Prior Art Process Mode ft./sec. to ft./sec. None Continuous Process Grinding by explosion Sound ore; not weathered; usually very hard rock Very high (2000-6000 psi.) Compressible fluid such as gas or vapor Fluid expansion causes explosion Accomplishes total disintegration or demolition and will need further treatment, i.e., flotation, to accomplish removal of impurities It is impossible to use a venturi to grind or shatter by explosion due to the high pressure and small orifice required. 1000 fL/sec.

Work by USBM on explosive shat tering of minerals, 1932-1933 Intermittent Process 25-100 psig., preferably 30-60 psig. to treat encrusted heterogeneous minerals in the manner I employ.

In connection with the description of my invention,

So far as I am aware, no one has utilized pressure of minerals, especially weathered heterogeneous miner- FIG. 2 is a more or less diagrammatic three-stage or continuous variation for decompression scalping, and specifically with reference to the treatment of weathered phosphate.

Referring to FIG. 1, in batch operation the system is filled with water through pump sump 5 with valve 7 open and valve 6 closed. Next, the sample is added at sump 5. Pump 1 causes the slurry to pass through valve 7 into venturi 2 and through throat 3 of the venturi. The pressure at venturi 2 is to 100 psig and beyond the throat 3 is 0 psig. When the material completes one pass through the venturi nozzle it is discharged by opening valve 6 and closing valve 7.

In semi-continuous testing the procedure is identical with the batch operation, except that the material is recycled for a predetermined amount of time equivalent to a number of passes through the nozzle. As in the batch or one pass system value 7 is open and valve 6 is closed during the recycle operation. An impingement plate 4 is optional.

TABLE II Calculated Iron and Aluminum Reduction Levels When Using An Average Rockland Phosphate Pebble* BPL** Pebble Pebble Product Overall BPL Final Fe A] (Fe Al) to Method Treated, Studied Studied Recovery, Content, BPL Ratio Impact crushing 100 Coarse & 68.0 88.7 2.25 0.0331

medium Rod mill & amine float 100 Coarse 70.0 75.0 2.30 0.0328 NaOl-I leaching 100 Coarse & 65.6 99.5 1.95 0.0298

medium Decompression scalping 100 Medium 68.0 89.0 1.78 0.0262

Average Pebble Quality: 65.7 BPL, 2.6% Fe & Al (from published prospect data) Bone phosphate of lime (triealcium phosphate) als, which comprises forming a slurry of particles of the mineral, subjecting the slurry to a pressure between about 25 psig. and 100 psig., passing the pressurized slurry through a nozzle to the atmosphere to provide sudden release of pressure, and then optionally but preferably, impinging the slurry onto a solid surface. The slurry may be formed, pressurized, and passed through the nozzle continuously.

In general, there is a difference in porosity and fria- A comparative study between standard approaches and decompression scalping (my invention) was made based on pilot-plant and bench-scale derived data and calculations using phosphate pebble. Table II illustrates final attainable iron and aluminum levels.

The invention will be further described with reference to FIGS. 1 and 2 in which FIG. 1 is a more or less diagrammatic illustration of a batch system for decompression scalping, and

Venturi 2 may be provided with different inserts which change the diameter at throat 3. Each nozzle opening sets a specific constant pressure in the system.

In operation, the treated phosphate pebble is passed through a series of screens to separate the cleaned pebble from the smaller mesh size material. This is best illustrated by reference to the continuous process threestage decompression scalping system shown in FIG. 2. In FIG. 2, the treated product from pump 32 passes to screen 34 where the +16 mesh pebble is removed and passed to storage. The 1 6 mesh portion then passes to a sizing section 36 where the 16 +150 mesh product is passed to the beneficiation plant 38 for additional phosphate recovery by flotation techniques. The -l 50 mesh portion is sent to disposal ponds. Treated product is obtained by adding water and weathered phosphate pebble, for example, to sump 20 for pumping by pump 22 through venturi 24 to be received by sump 26, and pumped by pump 28 to venturi 30, and successively to pump 32.

Screening at mesh sizes other than mentioned, and variations in equipment, are possible without departing from the teachings of my invention.

The following is a brief discussion of the operating variables affecting the process.

a. Pressure In the case of impurity removal from phosphate rock, the preferred pressure range upstream of the venturi is from 30 to 60 psig. The range from 60 to psig has not been studied in detail, but screen analysis shows 32.59% of the Fe O and 30.9% of the A1 with a 10.40% P 0 loss, in the 20 mesh fraction. The high iron and aluminum removal made possible by this method was obtained in spite of the abnormally low b. Temperatures 5 iron and aluminum content of the rock.

Decompression scalping is effective between 33 and 140F., with optimum results at the higher temperatures. Since the primary asset of this method is lowoperating and capital cost, it is not anticipated that Example H heating slurries could be justified, and, therefore, the Another 25 pounds of the same composite used in Processes would normally be Operated at ambem Example I was given three passes through a venturi slurry temperatureswith an outlet impact block. On this test as shown in PH v Table III 11.07% of the total sample reported to the Addltlon of aclds of bases to the aquews Pebble 20 mesh fraction containing 29.19% ofthe mo, and slurry assists the decompression scalping by removal of 3 4.3 4% of the A1203, with a 919% P205 10SS an additional 1020% iron and aluminum. Phosphoric acid plant effluent streams which are weakly acid and usually warm can also be used to enhance results. The pH of the slurry should generally be in the range of 0.5 Examples me to 4. Three equal portions of a 50-pound composite, rep- Examples I and L below, used a Single P (batch resenting 5,000 tons of Rockland medium pebble, were Operation) through the System at a P1essure Variation individually given 3-, 5-, and 10- second retention time from 20 to 60 p This batch technique was repeated passes in a semicontinuous system. The venturi was three times with cumulative results reported for each id d with a discharge impact block. Tabl IV Pass. Test results are given in Table marizes the reject possibilities. Fe O and A1 0 re- In the case of Examples III and IV, the pressure was mova] i ll cases was b t and if the 20 held at 30 psig, and the material recycled for a P mesh fraction is rejected. To the -l6 mesh fraction retermined time interval equivalent to a given number of t d -45% of the impurities, with a 25% P 0 loss. passes through the venturi. Test results are given in In this case, the rejected portion would require further Table IV. 30 beneficiation to minimize P 0 losses.

TABLE III Comparative Evaluation of Physical Classifications Medium Pebble Composite No. 3

Example No. 1 3-Pass Decompression Scalping (Batch System) (Weight P205 F5203 A1203 ACId Insol. Fraction Weight Anal. Dist Anal. Dist Anal. Dist. Anal. Dist.

Cumulative Head 100.00 31.1 1 100.00 1.13 100.00 1.45 100.00 8.79 100.00 +20 87.68 31.69 89.60 0.87 67.41 1.14 69.03 6.64 71.30 20+150 6.91 24.95 5.58 1.67 10.25 1.76 8.41 25.83 21.96 1 Pass, 150 2.31 29.20 2.17 3.75 7.64 4.28 9.66 9.16 2.59 2 Passes, -150 1.80 27.55 1.61 6.00 9.58 3.84 7.66 13.66 3.02 3 Passes, 150 1.30 28.86 1.04 5.33 5.12 3.08 5.24 8.13 1.13

Example No. 2 3-Pass Decompression Scalping W/Impact Blocks (Batch System) (Weight P 0 rep, A1 0 Acid Insol. Fraction Weight Anal. Dist. Anal. Dist. Anal. Dist. Anal. Dist.

Cumulative Head 100.00 31.15 100.00 1.08 100.00 1.45 100.00 8.65 100.00 +20 88.93 31.81 90.81 0.85 70.06 1.07 65.95 7.09 72.94 -20+150 7.25 24.62 5.73 1.39 9.36 1.95 9.82 27.70 23.23 1 Pass. 150 1.33 27.09 1.16 6.69 8.25 4.33 8.37 10.00 1.53 2 Passes, 150 1.07 27.89 0.96 5.86 5.84 4.06 7.83 9.10 1.12 3 Passes, 150 1.42 29.38 1.34 4.96 6.49 3.22 8.03 7.21 1.18

Example I Examples IVa and IVb Twenty-five pounds of a 50-pound composite, representing 5,000 tons of Rockland medium pebble, was given three passes through an open-end venturi (Mud Mixing Jet, by Mission Mfg. Co.) 12.38% of the total weight reported to the 20 mesh fraction. The fractions of +20 and -20+15O in Table III are the totals accumulated after three passes. Table III also shows Two equal portions of a 40-pound composite, representing 4,000 tons of Rockland medium pebble were run through the semicontinuous system at pressure of 30 psig. In the case of IVa, the pebble slurry was made with a phosphoric acid plant effluent slurry (pond water), and in the case of IUb, the pebble slurry was made with a 1.5% H SO solution. Results are also included in Table IV.

TABLE IV- Semicontinuous Decompression Rejected Fractions BPL Fe oa 1; A1 MgO Description Example Mesh Wt. Loss Rejected Rejected Rejected 10-sec. Retention lllc "l6 27.86" 25.81 41.13 45.57

S-sec. Pond'water combn. lVa l'6 19.51' 15.13 55.48 42.40 20.35 S-sec. Weak H 50 comhn.,; lVh l6 22.27 19.55 38.71 41.58 I 40.64 3-sec. Retention Illa -20 15.34 13.11 29.66 30.88 -sec. Retention lllb 2() 16.07: 13.73 29.73 36.13 29.83 10sec. Retention lllc 20.17 17.83, 35.45 39.12

5sec. Pond water combn. lVa 20 12.39 I 7.78 51.34 36.80 13.82 5-sec. Weak H- ,SO comhn. lVb -20 14.34 1 1 .56 "32.17 34.07 34.64 3-sec. Retention 111a 150 4.65 4.23 18.65 18.01 S-sec. Retention lllb 150 5.51 5.00 20.32 23.81 21.69 10-sec. Retention lllc l50 6.21 5.75 22.65 23.40

5-sec. Pond water combn; lVa l'50 5.10 2.16 -46.68 28.61 8.42 5-sec. Pond water combn. lVa Leachate 3.21 0.74 40.24 18.27 0.0 S-sec. Weak H 80 combn. lVh l50 2.93 2.88 21.33 18.42 26.76 S-sec. Weak 1-l So combn. lVb Leachate 1.22 20.76

The pond water action was extremely effective on this particular rock composite Fe O removed was 55.48, 51.34, and 46.68%, depending on whether the 1 6 mesh, the 20 mesh, or the l50 mesh screen size was chosen for rejection. BPL losses were 15.13, 7.78, and 2.16% repectively.

A significant observation is the variation in rejection depending on whether pond water or H SO is the acid source. Pond water treatment was not as effective in removing MgO as H 80 treatment.

Example V Four samples of phosphate pebble were obtained from phosphate minig companies in Central Florida. Each sample was subjected to psi. semicontinuous decompression scalping, which included use of an impact block at the venturi discharge. Samples C and D were relatively hard pebble with only slight evidence of a weathered crust. The products from decompression scalping were screened on a ISO-mesh screen and the 150 mesh portion discarded. Table V indicates the level of phosphate loss and the R 0 rejection to the 150 mesh fraction.

TABLE V of Total Feed Pebble Phosphate F6 0, A1 0 MgO Sample Loss Rejected Rejected Rejected A 15.3 35.2 46.9 45.7 B 16.6 25.2 33.1 23.4 C 2.42 6.15 4.09 8.75 D 3.90 10.17 9.95 7.87

deposits can be classified into two groups those in 6 which the weathered crust contains the valuable mineral such as NiO and A1 O bearing laterities, and

those which involve impurity removal to upgrade the valuable mineral; e.g., phosphate rock. A few specific ore bodies are discussed below to illustrate this point.

Orskany Iron Ore, of Virginia is made up of earthy masses and rounded concretions of fibrous limonite filled with clay or sand. This ore is subject to a rough concentration in log washers in order to remove the clay. Decompression in nozzles could be used to improve concentration.

Cuban ironand nickel-bearing laterities occur as residual mantles resulting from the weathering of serpentine, and for the most part lie on plateaus at rather high elevations. Near the surface the material is earthy and dark red, sometimes cemented, with shot-like lumps of hematite. Underneath lie yellowish ores changing into decomposed and soft serpentine, irregularly crossed by layers of chert.

After primary crushing and decompression scalping, a hard low-iron serpentinic fraction could be separated for special treatment with solid reductants since it does not yield a high nickel extraction on the standard gaseous reduction step.

Lateritic deposits similar to the above are found in India, Africa, Guatemala, Santa Domingo, Macedonia, Borneo, and the Philippines.

The residual manganese deposits of the Appalachian Region occur in a decomposed surface zone of many different rocks. At the Crimera deposit, in Virginia, ore lumps are found within a clay stratum. After primary washing, crushing, and desliming. selective removal of cemented impurities and indurated clay could be achieved by decompression scalping.

Brazilian Manganese Deposits at Minas Geraes are also residual ores derived from the weathering of lenses in the crystalline schists containing rhodochrosite. A large portion of these ores take the form of psilomelane concretions in the soft decomposed rock. Decompression acid scrubbing or leaching would be necessary to remove cemented decomposed rock from granular minerals.

A commercially important concentration of nickel was formed in New Caledonia by the action of weathering of serpentines and periodities. The clay-rich ore, containing 57% NiO is by now well depleted. Another section of the island contains lower grade deposits of partially decomposed serpentine. Here the objective of decompression-acid scrubbing would be upgrading by scalping a hard coarse fraction.

Finally, several systems presently using attrition scrubbing could economically benefit by the considerably lower retention time required by the decompression scalping system. Typical applications are (l) removal of iron stains from glass sand, (2) removal of slime coating and cementing material from potash, (3) liberation of granular materials from cementing clays, and (4) removal of lime from sandstone.

Even where lengthy attrition scrubbing is mandatory due to special reasons, a step of decompression scalping would considerably reduce the number and/or size of equipment required.

My invention is not limited to the specific examples and illustrations above. It may be otherwise variously practiced within the scope of the following claims:

I claim:

1. Method of separating porous lateritic weathered ore particles into crust and core portions comprising forming a liquid slurry thereof, subjecting the slurry to a pressure between 25 and 100 psig, and releasing the pressure to the atmosphere through a nozzle.

2. Method of claim 1 followed by impingement of the slurry at a velocity of 60 to ft./sec. on a hard surface.

3. Method of separating the weathered crust from the core of porous lateritic weathered ore particles comprising forming a liquid slurry thereof in water andsubjecting the particles to decompression scalping at a pressure between 25 and psig.

4. Method of claim 3 in which the pressure is between 30 and 60 psig.

5. Method of claim 3 followed by shattering of the ore.

6. Method of claim 3 in which the ore particles are phosphate ore particles.

7. Method of claim 1 in which the slurry is continuously formed, subjected to pressure, and passed 

1. METHOD OF SEPARATING POROUS LATERITIC WEATHERED ORE PARTICLES INTO CURST AND CORE PORTIONS COMPRISING FORMING A LIQUID SLURRY THEREOF, SUBJECTING THE SLURRY TO A PRESSURE BETWEEN 25 AND 100 PSIG, AND RELEASING THE PRESSURE TO THE ATMOSPHERE THROUGH A NOZZLE.
 2. Method of claim 1 followed by impingement of the slurry at a velocity of 60 to 90 ft./sec. on a hard surface.
 3. Method of separating the weathered crust from the core of porous lateritic weathered ore particles comprising forming a liquid slurry thereof in water and subjecting the particles to decompression scalping at a pressure between 25 and 100 psig.
 4. Method of claim 3 in which the pressure is between 30 and 60 psig.
 5. Method of claim 3 followed by shattering of the ore.
 6. Method of claim 3 in which the ore particles are phosphate ore particles.
 7. Method of claim 1 in which the slurry is continuously formed, subjected to pressure, and passed through a nozzle. 